Concurrent engineering aims to integrate product design and manufacturing cycles in a systematic way to facilitate the swift, cost-effective progression of new products from raw concept to end customer.
Traditionally, when designing a new product, a team of designers usually participate in what is known as a product development cycle. In general terms, the first stage in designing a new product is that of concept design, in which overall needs and aims are addressed.
Next is the initial design stage. The initial design stage comprises steps of designing the part, then choosing the materials and determining the process to make the part, then designing the tool to make the part. For example, if the part is to be a computer keyboard, first the size and shape of the keyboard (i.e., the part) is determined by a part engineer. Next, when the part has been designed, a second engineer determines the design of the tool that can be used to make the keyboard. Separately, a process engineer determines the materials and process to make the part, for example, whether the part is to be made of plastic, metal or some other material, the properties of the material, the process to be used to make the keyboard (e.g., casting, injection molding, forming, etc.) what are the process parameters and the rate of production of the process.
The next stage, after a prototype of the part has been made, is revising the design. The above steps of part, tool and process design are repeated until a satisfactory part is produced, both as to design and cost of production.
Traditionally, each of the above steps are carried out sequentially, usually by different people. One person may design the part, another the tool, and a third the process. Collaboration between these designers is usually minimal. Where many revisions have to be made, numerous iterations are needed and a long period of time passes until a satisfactory part is produced.
Using present design approaches and tools, there is incomplete knowledge of the required manufacturing steps to produce the part, and inadequate consideration of the variety of other downstream influences that shape time to market, marketplace acceptance, and product longevity. Often neglected, but of importance in part design are the constraints added by environmental concerns relative to the product and its process of fabrication. These flaws lead to a multitude of costly and time consuming design reworks or difficult process modifications as unanticipated problems must be rectified.
Computer tools exist to help each designer carry out his or her function in the design process. For example, Computer-Aided Drafting (CAD) tools exist for creating two and three-dimensional drawings of the part. Material properties databases exist to help determine the composition of the part. CAD/CAM (computer-aided drafting/computer-aided manufacturing) tools exist that assist in tool design. Various tools exist for process design, for example, mould filling tools can be used in designing a mould injection process and simulations can be used in designing a sheet metal cutting and forming process. However, there is very limited interaction between the tools used at each step in the design process.
Existing tools may be useful in evaluating given designs. But they are unable to perform concurrent integrated design of part, tool and process. In effect, they automate the traditional sequential approach to design. For example, consider the field of plastic molding. Computer based tools now available to the molded part designer (e.g., mold filing tools, part cooling tools, shrink-warp predictions programs, structural FEM, even CAD/CAM systems) analyze the part as a whole. They attempt to predict part characteristics given full descriptions of geometry and process conditions. However, such tools can only be used in analysis functions; they do not synthesize new forms that achieve the functionality dictated by product use requirements. At best, a well integrated set of analysis tools may ultimately serve as a "virtual prototyping" environment, where leading candidates among various design concepts can be evaluated. However, unless rapid trial and error is offered as methodology for design, there remains a void to be filled at the conceptual design stage. The designer needs guidance to ensure that all design alternatives, from the outset, incorporate good engineering practice from the standpoint of all disciplines that contribute to the product lifecycle.
The way existing design tools represent information and communicate with each other is often not consistent. Moreover, the design tools used at the stages of part design, tool design and process design do not, because of the different representations used by these tools, communicate well with each other.
For example, CAD application programs create views of objects in two or three dimensions, presenting the object as a wire-frame "skeleton" or sometimes as a more substantial model with shaded surfaces. Some CAD programs can also rotate or resize models, show interior views, and generate simple lists of materials required for construction.
The drawings output by CAD systems do not comprise engineering knowledge. CAD systems are used to produce detailed engineering drawings when part geometry is known both qualitatively and quantitatively--i.e., after conceptual design is complete. Further, CAD systems generate the part geometry data used by subsequent analysis software to simulate part performance. But the part designer is not assisted in what to do to design a part that meets all performance requirements, including cost and manufacturability. It is as the design for the part is formulated that guidance is needed to ensure that all design alternatives incorporate good engineering practice from the standpoint of each contributing discipline: i.e., materials, part geometry, tooling, process and cost analysis.
CAD/CAM application programs can be used in both the design and manufacture of a product. With CAD/CAM, a product, such as a machine part, is designed with a CAD program, and the finished design is translated into a set of instructions that can be transmitted to and used by the machines dedicated to fabrication, assembly, and process control.
CAD and CAD/CAM systems are limited to address only the form of the design; functional requirements are the responsibility of the designer, not the system.
The knowledge used and needed when the part, tool and process are being designed typically has been represented in different ways. The notations for the part design, tool design and process design usually differ and are often not compatible. For example, when using a CAD system to design a part, knowledge of the process to make the part (for example, knowledge about die casting a metal part or about the flow of plastic) is not reflected in the part design in the CAD system. Thus, the design of a part may, although geometrically correct, not be a satisfactory design when considering the process used to make the part.
Further, the representation of the part in the CAD system uses geometrical primitives that are not useful for tool and process design. The geometrical primitives in a CAD system are usually points and lines, not geometrical shapes that are engineering concepts representing the components of a part. For example, a CAD drawing for a box is effectively one shape (the box) comprising lines, and not made from the engineering components that make up the box such as the base and side walls.
If the computer is to assist in the act of design, then it must reason about the part of a level of abstraction that is close to that of the designer. Today's software is designed to create geometry, but form is an ambiguous indicator of the designer's intent. Many things look alike, but it is their end use or functionality that dictates the appropriate set of rules by which size and shape can be computed. The engineering constraints and design relationships for a load bearing wall are different from those of a non-loadbearing internal partition. Ribs used for stiffening a wall are subject to completely different considerations from those used to dissipate heat, and sizing a hole to accommodate a self-tapping screw differs from sizing one to allow passage for a wire harness. Yet in each of the preceding scenarios it would be difficult, it not impossible, to judge the purpose of the geometric construct solely by its form or placement in the part.
No existing system enables complete product representation, where the product representation includes part geometry and functional information about the part. To do this requires a higher level of design representation than the typical CAD-type geometric products provide. Feature-based modeling techniques that have been proposed as a modeling technique have limitations. First, the designer is restricted to a finite number of pro-defined geometric shapes, and this may not be sufficient to capture the complete behavior of the part in terms of its functionalities. Another drawback is the difficulty in decomposing complex designs into a basic feature vocabulary. These shortcomings make it difficult for an intelligent design system to completely model a part and its function, and properly reason about the designer's intent. A new type of feature representation is required to address these limitations.
Automated processes are known for certain elements of the design process, but these are of limited application. For example, Flexible Computer Integrated Manufacturing (FCIM) is a known automated approach to produce a variety of parts for a given automated system. Quality Functional Deployment (QFD) is a known process that is used to help determine functional requirements from customer needs. Many attempts have been made to develop intelligent design systems using different implementations strategies. One implementation method is to integrate a commercial CAD system with an expert system inference engine. Some have attempted to integrate an expert system shell with a solid modeler. Another known approach is to use an existing knowledge-based engineering tool which already provides geometric modeling capabilities and mechanisms for embedding heuristic knowledge in the form of rules and methods. Systems developed using the above mentioned approaches have shortcomings due to the limitations of the commercial software packages which they are built around. None of these known tools or processes fully integrate part, tool and process design. Further, no known system represents all the knowledge for part, tool and process design in a systematic way so that this knowledge can be used in all stages of the design process.
Current computer-based tools require complete description of the part geometry as well as all relevant boundary conditions on the state variables of the system (for example, loads and constraints for stress, molding temperatures and gate pressure or flow rate for filing). A computer simulation may then predict the response of the part to this imposed environment. With sufficient accuracy in the underlying material response relationships (e.g. modules, density, viscosity) these tools could be viewed as an element of prototyping. If the process begins with molding simulation, and then the part dimensions are corrected for shrink and warp, as well as the anisotropic distribution of properties arising from flow orientation effects and if transverse morphological variations are fed into the structural analysis, the resulting deflections under load and stress patterns could provide rapid confirmation of the design and the means for design optimization. Such a strategy, however, fails to provide for a basic need critical to the rapid evolution of design concepts into detailed designs; the initial specification of geometry and process conditions that are suitable to meet the design requirements.
Present design practices are illustrated in FIG. 1 (prior art), which shows the sequential nature of the design and fabrication steps. The functional elements of part, tool, and process are handled in a serial fashion that necessitates considerable prototyping to ensure consistency of the final part with the designer's expectations. The role of computing aides and tools, as discussed above, only support the individual functional domains, and do little to bring downstream influences up to higher design levels.
As shown in FIG. 1, the first step of the typical prior art methods is to determine customer requirements (step 2). Once a product concept is decided upon, a preliminary design of the past is made (step 4). Usually, a sketch is made of the proposed part. If the sketch is approved (step 6), a detailed part design can be developed (step 8). A CAD system 28, a database system 30 and a Finite Element Method (FEM) 32 can be used to produce a detailed part drawing. If this drawing is approved (step 10), a prototype tool design is developed (step 12). A CAD system and a mold-filling analysis (MF) 34 can be used to produce a detailed tool drawing. A CAM tool 36 is used at the tool fabrication step (step 14). Next, the process specification is decided upon (step 16), often with the aid of a MF. Actual manufacturing trials are carried out (step 18), and if approved (step 20), a product tool design step (step 22), a tool fabrication step (step 24) and product manufacturing (step 26) are carried out. One should note the sequential nature of the prior art design process, and the many revisions and tests that must be undertaken along the way to obtaining correct and feasible part, tool and process designs.
Typically, at steps 4 and 8, parts are conceived for form and function only, and designed with the assumption of uniformly distributed properties. For example, when designing parts that will be created using injection molding techniques, modifications like draft angle and corner radii are left as afterthoughts for the tooling engineer (at steps 12 and 14), and the ramifications of flow orientation and transverse morphology that result from the processing step (step 16) are rarely considered, if at all. The price paid is one of over-design to allow adequate safety margins, excessive rework of part, tooling or process to accommodate unanticipated interactions, and even outright elimination of plastics as candidate materials of construction. In any event, the result translates to dollars wasted in materials and resources, and profits lost in delayed time to market.